Transfer assembly for manufacturing electronic devices

ABSTRACT

A method for assembling a device. The method comprises placing a functional element in a first opening formed in a template substrate and transferring the functional element to a device substrate having a second opening formed therein wherein the functional element is held within the second opening and against an adhesive film coupled to the device substrate.

RELATED APPLICATION

This application is related to and claims the benefit of U.S.Provisional Patent application serial number 60/471,422 filed May 16,2003, which is hereby incorporated by reference in its entirety.

GOVERNMENT RIGHT

The United States government may have certain rights to the presentapplication since the present application may be involved in at leastone government contract having the following reference: DefenseMicroelectronics Activity, Contract DMEA90-03-2-0303.

FIELD

The present invention relates generally to the field of fabricatingelectronic devices with small functional elements depositing in varioussubstrates and apparatuses comprising these electronic devices.

BACKGROUND

For the fabrication of many electronic devices such as displays or radiofrequency identification (RFID) tags, there is a need to distributefunctional elements such as integrated circuit chips across large areasubstrates. The manufacturing of these devices is moving toward using aroll-to-roll processing. In many cases, the majority of the substratearea will not contain active circuitry or functional elements and thefunctional elements will occupy only a small fraction of the substrates'active areas. Functional elements are typically deposited into asubstrate using pick-and-place or a fluidic-self assembly process. Theseprocesses are typically expensive. Because of the relatively sparsepopulation of the functional elements on the substrates, it may beadvantageous to assemble the functional elements in a differentsubstrate and transfer to the substrates used for the devices.

SUMMARY

Embodiments of the present invention pertain to a method of transferringfunctional elements deposited in a template substrate to a devicesubstrate.

In one aspect, an exemplary method of transferring includes removing atleast one functional element from a second substrate and transferringthe functional block to a first substrate. The first substrate includesan adhesive layer deposited on top of the first substrate, and at leastone opening. The functional element is transferred from the secondsubstrate into the opening and held in the opening against the adhesive.The method further includes making interconnection to the functionalelement.

In another aspect, another exemplary method is similar to the methodabove but the adhesive layer also serves as a dielectric layer. Inanother aspect, the method is similar to the method above but vias arealso created into the adhesive layer to establish electrical connectionfor the functional element.

In another aspect, an exemplary method includes using FSA to deposit aplurality of functional elements into the second substrate. Thefunctional elements are arranged in a densely packed array and at leastone functional block is selected from the array and transferred to thefirst substrate.

The second substrate is selected from a group consisting of a siliconwafer, a plastic film, a glass sheet, or a multilayer film comprisingthese materials.

Another aspect of the invention pertains to exemplary systems forforming electronic assemblies. An exemplary system includes a firsttransfer assembly station that includes a transfer mechanism, a firstweb line that supports a first substrate which has at least one openingcut therethrough, a second web line that supports a second substratethat includes arrays of functional elements packed therein, and aregistration station to align the first web line over the second webline such that the opening is aligned over one functional element. Thetransfer mechanism is configured to transfer the functional element tothe first substrate. The transfer mechanism includes a transfer headthat can be an inflatable bladder, pins, or a shaped plate withprotrusions.

In another aspect, another exemplary system further includes a treatmentstation that uses one of heat, chemicals, light, or radiation toactivate an adhesive material deposited on the first substrate to enablethe transferring of at least one function elements from the secondsubstrate into the openings in the first substrate. The system may alsoinclude an X–Y alignment stage for holding the second substrate.

In another aspect, an exemplary method for assembling a device comprisesplacing a plurality of functional elements in a corresponding pluralityof first openings formed in a first substrate and transferring only aportion of the plurality of functional elements to a second substratehaving at least one second opening. In yet another aspect, the placingof the functional elements in the corresponding plurality of firstopenings is accomplished via a fluid self assembly process. A slurry offunctional elements is created and dispensed over the first substrateand the functional elements become disposed in the first openings. Thetransferring of only a portion of the plurality of functional elementsto the second substrate comprises preventing at least one functionalelement from being transferred to the second substrate. In yet anotheraspect, the method further comprises aligning the first substrate to thesecond substrate so that only the portion is transferred. And in yetanother aspect, the method further includes at least two transferring.The first transferring occurs at a first time and wherein the methodfurther comprises a further transferring of another portion of theplurality of functional elements from the first substrate to the secondsubstrate.

The exemplary methods result in an electronic assembly which, in oneexemplary embodiment, a functional element is held against an adhesivefilm in an opening formed in a device substrate wherein the adhesivefilm is laminated to the device substrate. The functional element isfirst deposited in a template substrate and transferred to the devicesubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of punched-through substrate which may bea web substrate (e.g., roll to roll processing system).

FIG. 2 illustrates an example of punched-through substrate (e.g., a websubstrate) having an adhesive layer deposited thereon.

FIG. 3 illustrates a re-usable substrate having functional elementsdeposited therein, for example by using a Fluidic Self-Assembly (FSA)process.

FIG. 4 illustrates an exemplary embodiment of transferring at least onefunctional element from the re-usable substrate (e.g., there is only apartial transfer of elements from one substrate to another substrate).

FIG. 5 illustrates an exemplary embodiment where at least one functionalelement has been transferred to the punched-through web substrate shownin FIGS. 1–2.

FIG. 6 illustrates a section of a plurality of functional elementstransferred to the punched-through web substrate.

FIGS. 7–13 illustrate exemplary embodiments of creating electricalcontacts to the functional elements.

FIG. 14 illustrate an exemplary scheme of a web station that assemblesfunctional elements to the punched through web substrate.

FIG. 15 illustrate another exemplary scheme of a web station thatassembles functional elements to the punched through web substrate.

FIGS. 16–17 illustrate another exemplary embodiment of transferringfunctional elements from a re-usable substrate to another substrate.

DETAILED DESCRIPTION

In several types of integrated circuit fabrication and application, itis advantageous to form the integrated circuit elements in a denselypacked array, and then transfer these elements to another surface, wherethe spacing and density can be quite different than the spacing anddensity in the densely packed array.

For example, Fluidic Self-Assembly (FSA) can be used to place functionalelements such as integrated circuit elements (e.g., each functionalelement may be an integrated circuit) in receptor sites in a substrate.If the functional elements are the control elements in a radio frequencyidentification tag, then to function properly each of the functionalelements must be electrically connected to an antenna element. In oneembodiment, each of the functional elements is less than 1 mm on a side,while an antenna element is several square centimeters in area. It ispossible to perform FSA on a substrate such that one functional elementsis deposited on a web area several square centimeters in area, and thenforming the antenna on that web. Such a process can be slow,inefficient, and expensive, however, making the FSA process the ratelimiting step.

Some embodiments of the present invention relates to improved processesthat including using FSA to place functional elements in an area that isapproximately 1 square centimeter in area, and providing electricalcontact pads on the receiving web. This smaller assembly, called astrap, is then singulated and attached to an antenna, the antenna beingseveral square centimeters in area. The strap assembly is described in apatent application Ser. No. 09/872,985, now U.S. Pat. No. 6,606,247,which is incorporated herein by reference.

In one embodiment, we perform FSA to create a densely-packed array offunctional elements, which are placed in receptors spaced very closelytogether on a second substrate. Each of the functional elements may bean integrated circuit formed in a semiconductor substrate, such as anintegrated circuit (IC) which forms part of a radio frequency (RF)Identification tag or (“RFID”). The second substrate can be a plasticfilm or sheet, it could also be constructed out of an expensive,reusable material that provides superior performance for FSA, such as asilicon wafer. We then perform at least one transfer step that transferseach individual functional element to a first substrate. In the firstsubstrate, the functional elements are spaced further apart and arrangeddifferently than in the initial densely-packed array on the secondsubstrate. The first substrate does not need to be of high quality andexpensive so as to be optimal for FSA as the second substrate (and thusthe first substrate need not be as expensive as the second substrate).

The transfer process allows for very efficient use of FSA to assemblesmall integrated circuit elements in a second substrate and thenefficiently transfer them to a first substrate. The second substrate isoptimized to provide efficient FSA, while the first substrate isoptimized for the final form of the application. The first substrate canbe a substrate for a device that incorporates the IC elements. Such aprocess is superior to traditional pick and place methods, in which arobot handles an individual integrated circuit element to place it onone substrate. Additionally, the exemplary embodiments also allow forparallel processing of functional elements (rather than the serialmethod in pick and place), and can efficiently handle functionalelements in the range of 10 microns on a side to 10 mm on a side. Theprocess should increase the throughput of an existing FSA manufacturingprocess line by up to an order of magnitude.

In one embodiment, functional elements are deposited to a substrate in atwo-step process: firstly, use FSA to deposit the functional elements(e.g., blocks) into a second substrate and then, secondly, transfer theblocks from the second substrate to deposit the blocks into a firstsubstrate. As mentioned above, the second substrate typically (but notnecessarily in all embodiments) has the functional elements arranged ina densely packed array. The first substrate has the functional elementsarranged in the final form that is practical for a particular electronicdevice or application (such as RFID tag or an electronic display).

In FIG. 3, functional elements 102 are assembled on a second substrate104 which may be is referred to as a “re-usable substrate” containingreceptor sites 106 that are spaced more densely than the final productrequires. The functional elements 102 are transferred many at a time toa first substrate 108, which may have a web (substantially continuous)format such as the roll to roll web format which is often used to makepaper, etc. The first substrate 108 may have a form of a plastic web onwhich further lamination and metalization could occur. Alternatively,the functional elements 102 could come straight from a wafer that hasintegrated circuits formed thereon, as described below.

As illustrated in FIG. 1, the first substrate 108 comprises an array ofopenings or holes 110 “punched” through the web or material which formsthe first substrate. The first substrate 108 may be referred to as a“punched web” in many instances of this discussion. In this example, thehole 110 is completely (rather than a partial opening) through the firstsubstrate. The arrangement of the holes 110 would be the arrangementrequired of the final product. Prior to the transfer process, anadhesive film 112, which in one embodiment is an adhesive film 112 thatcould be used as a dielectric material, is laminated to the punched web.During the transfer process, the laminated, punched web is positionedover the filled re-usable substrate with the adhesive film on the top,sticky side down, such that the punched web is between the adhesive onthe laminate and the filled re-usable substrate, except where there is apunched hole in the web as illustrated in FIG. 2. The adhesive could bea pressure sensitive adhesive (PSA), a heat-activated adhesive, achemically-activated adhesive, a microwave or radio-frequency activatedadhesive, a photochemically-activated adhesive, a radiation-activatedadhesive, or other types of suitable adhesive.

In one embodiment, the receptor sites 106 in the second substrate 104are arranged in one or more regular patterns designed to match thepattern of the openings 110 in the first substrate 108. In oneembodiment, the receptor sites 106 in the second substrate 104 are inone or more arrays designed to match the array pattern of the openings110 in the first substrate 108. In another embodiment, the receptorsites 106 in the second substrate 104 are in an array in which the pitchbetween the openings in either of two orthogonal directions is equal tothe corresponding pitch of the openings 110 divided by an integernumber.

In FIG. 4, a mechanical transfer 114 (pins, deformable bladder, or otherdevices as described below) is used to pick up the functional elements102 and transfer them to the first substrate 108. The adhesive film 112can be a type that can be activated locally heat, light, or otherconventional methods. As shown in FIG. 4, only some of the functionalelements are transferred at one point in time (rather than all at thesame time), and additional transfers may be subsequently performed atlater times.

The web may be located with respect to the second substrate 104 suchthat each hole 110 on the first substrate 108 is above a functionalelement 102 on the filled re-usable substrate 104. In FIG. 4, to do thetransfer process, the adhesive film 112 is pressed through the hole 110on the first substrate 108 to make contact with at least one functionalelement 102. When the pressure is removed on the adhesive film 112, thefilm returns to its original position with respect to the punched web orfirst substrate 108, and the transferred functional elements 102 are inthe holes 110 in the punched web or first substrate 108 as illustratedin FIG. 5. An entire frame, or multiple frames, of functional elements102 could be transferred at once with this process. FIG. 6 illustrates asection of a transferred frame of functional elements 102 to the firstsubstrate 108.

Once the transfer process is completed, the first substrate 108 isindexed relative to the second substrate 104 forward to the next frameof available (unfilled) punched holes. At the same time, the filled,reusable substrate 104 may be indexed such that another frame offunctional elements 102 are ready to be transferred. On the punched web108 that now contains functional elements 102, there will be a gap 116in the hole 110 between the side of the hole 110 and the functionalelements 102, as seen in FIGS. 5–6. The gap 116 may or may not be filledin. If necessary, the gap 116 can be filled with a UV epoxy or otherthermoset resin. Furthermore, if necessary, a laminate could be appliedto the back of the first substrate 108 to lock the functional elements102 into place. Alternatively, it may not be necessary to fill the gap116 at all.

In some embodiments, the gaps 116 are filled and the first substrate 108does not include a back laminate to lock the functional elements 102 inplace. In some embodiments, the gaps 116 are not filled and the firstsubstrate 108 includes a back laminate, (not shown), which can be madeof PSA or a thermal material to lock the functional elements 102 inplace. In yet some other embodiments, the gaps 116 are filled and thefirst substrate 108 includes a back laminate to lock the functionalelements 102 in place.

Once the functional elements 102 are transferred to the first substrate,which may be a receiving web, it is usually necessary to provideelectrical contacts to one or more contact pads on the functionalelements 102 if the functional elements include electrical circuitrywhich requires an external connection. For the purposes of thisdiscussion, we define the “top” of the functional elements 102 as theside facing up, side 118 (FIG. 3), after it has been deposited (throughfor example an FSA process) into the reusable, densely-filled substrate104. The transfer adhesive 112 then adheres to this top functionalelements 102 surface 118.

In the case of functional elements 102 in which the contacts are all onthe top surface 118, it is necessary to provide a way to form anelectrical contact to the contacts once the transfer to the firstsubstrate or receiving web has taken place. One way of providing thiscontact is to form via holes 120 in the adhesive layer 112 over thecontact pads 122 on the functional elements 102, and followed by ametallization process (forming conductive traces 124) to forminterconnections as illustrated in FIGS. 7–8. Vias 120 formation canoccur by a number of conventional methods, including laser drilling orphotolithographic etching. Suitable conductors can include metallicfilms, conductive polymers, or inks filled with conductive particles.

The metallization 124 can either be a subtractive process (usingetching/lithography or laser ablation) on a metal film, or an additiveprocess (such as printing) metal traces.

Via 120 formation and metallization 124 can occur after the transferprocess.

Alternatively, the vias 120 could be formed in the adhesive layer 112before the transferring of the functional elements 102, and theformation of the metallization 124.

In another embodiment, the vias 120 could be formed in the adhesivelayer 112 after the adhesive layer 112 has picked up the functionalelements 102, but before the actual transfer to the first substrate 108.The formation of the metallization 124 would occur after transfer to thefirst substrate 108.

In another embodiment, one or more contact pads 126 will be positionedon the bottom of the functional elements 102 as illustrated in FIG. 9.In this case electrical contact can be made directly onto the functionalelements 102 after transfer, as they will be exposed on the surface ofthe substrate 108.

Alternatively, a thin polymer layer can be laminated or otherwise formedon top of the first substrate 108 containing the functional elements102, with the purpose of locking in the functional elements 102 onto thefirst substrate 108, or otherwise protecting them. In this embodiment,the vias 120 can be subsequently formed to allow for contact to thebottom on the functional elements 102, as described above.

In another embodiment, functional elements 102 contain both top andbottom contacts (122 and 126) as illustrated in FIG. 10. In this case amixture of the above processes can be used to form contacts.

In another embodiment, the adhesive film 112 can comprise ananisotropically-conductive adhesive, providing for electrical contactthrough the adhesive film that is essentially self-aligned with thefunctional elements 102 contact pads. Subsequent electricalinterconnection can then be made to the opposing side of theanisotropically conductive adhesive film 112.

For certain applications (such as radio frequency identification tags)it may not be necessary to provide a direct resistive electricalcontact, but it may be sufficient to provide a capacitive or inductiveelectrical contact to the functional elements 102 contact pads. In thiscase the thickness of the adhesive, and subsequent conductor placement,can be arranged to allow for these types of connections.

In one embodiment, the vias 120 could be drilled through the top layerbefore transferring the functional elements 102.

Exemplary embodiments of the present invention process can be applied toone or more different types of the functional elements 102. For example,the transfer process described above can be done with one type of thefunctional elements 102. Then the first substrate or web could beindexed forward to a second transfer station which could transfer into asecond set of locations either more of the first type of device, or asecond type of device. This index and transfer process could be repeatedfor as many times as necessary to place all of the desired devices intheir respective locations. This ability to repeat the index andtransfer process solves at least two potential problems. First, it maybe necessary, for either product function or process economics reasons,to have the same devices placed on the web in a pattern that is notconducive to completing in one transfer process step. Second, theproduct may require the functional elements 102 with differentfunctionality and/or different material. Third, the product may requirethe functional elements 102 to have different shapes or sizes. Forexample, the first transfer step could transfer the functional elements102 with digital circuitry, while the next transfer step could transferdevices with analog circuitry. Alternatively, the first transfer stepcould transfer the functional elements 102 with RF communicationcapabilities, while the second transfer step could transfer thefunctional elements 102 with sensing capabilities. Potentially,additional transfer steps could transfer devices with energy storage anddelivery capabilities. In yet another example, the first transfer stepcould transfer individual pixel drivers for a display, while the secondtransfer step could transfer a display driver chip IC which drives andcontrols the pixel drivers. Or the first transfer step could transferGaAs IC's, while the second transfer step could transfer silicon IC's.There are plenty of additional examples of how having two or moredevices would be beneficial. The last example does point out animportant feature of the process, which is that it could work withdevices fabricated from any material, including but not limited to,silicon, silicon-on-sapphire, silicon-on-insulator, gallium arsenide,silicon carbide, gallium nitride on silicon, etc.

In another embodiment, the transferred material is a diced or otherwisesingulated thin film transistor (TFT) circuit on a flexible substratesuch as metal foil or high temperature plastic, or a rigid substratesuch as glass or quartz.

Whether there are one or multiple transfer steps in the process, afterthe devices are transferred, there need to be openings, called “vias”,for electrical connections to the pads on the tops of the devices ifexternal electrical connections are required for the devices to work.These openings could be made either before the transfer process, orafter the transfer process. Before the transfer process, the vias couldbe made by either laser drilling, wet etching, plasma etching, punching,or mechanically drilling the adhesive film in the appropriate locationsto make contact with the devices after they are transferred. The viascould also be made after the transfer process, in which case it ispreferable that the adhesive film used in the transfer process be eitherlaser drillable or etchable.

In another embodiment, the adhesive film 112 can be a temporaryadhesive. Once the gap is filled with the UV cured polymer or thermosetpolymer or thermoplastic resin, the adhesive film can be pealed off.Then the functional elements 102 connections can be made by directlyscreen printing silver ink onto the functional elements 102 contactpads. This temporary adhesive could be UV release tape. This processcould eliminate the need for a via. In the case where it is necessary toreduce the capacitance caused by the metal interconnect over thefunctional element, tall (5–25um) bumped interconnection pads on thefunctional elements could be used. The adhesive film would make contactwith these bumped pads. The gap filler (UV-cured polymer, thermoset, orthermoplastic resin) would underfill between the adhesive film and thetop of the device. Once again, when the adhesive film is removed, bumpedmetal pads are left, surrounded by a thick film dielectric, and the needfor the formation of a via is eliminated.

Options for vias include no via, photo vias with laminate, and laservias with laminate.

The assembly of the exemplary embodiments could also be created fromfunctional elements 102 (e.g., IC chips) that are thinned and diced inwafer format (e.g., etched and coupled to a handle substrate), andtemporarily held in place on a dicing tape or other adhesives. Theadhesive laminated, punched web could be placed over the wafer, and anentire frame could be transferred at once. In one embodiment, asubstrate 108 with openings 110 and adhesive film 140 laminated to thesubstrate 108 is placed over the wafer that have the functional elements102 that are thinned and diced in the wafer format. The adhesive film140 is then pressed through the openings to cause the functionalelements 102 to be transferred over to the substrate 108. To reduce theadhesion of the dicing tape, UV release dicing tape could be used, andthe UV exposure could be either a flood exposure, or through a stencilor mask so that only the adhesive touching the chips that are to betransferred is UV-treated.

In an alternative embodiment, one or more of the functional elements 102are transferred from the wafer that have the functional elements 102that are thinned and diced in the wafer format (e.g., etched anddisposed on or coupled to a handle substrate) onto a template substrate(e.g., a second substrate 104). In one embodiment, the functionalelements 102 are singulated, isolated, or separated after being formedinto their particular shapes (e.g., thinned). The functional elements102 are also coupled to or otherwise disposed on the handle substratewhich are then transferred onto the template substrate. The functionalelements 102 are then transferred again onto a device substrate (e.g., afirst substrate 108). In one embodiment, the template substrate isfabricated with a pattern of receptor sites that matches the pattern offunctional elements 102 that are formed on the wafer. The templatesubstrate is then placed on the wafer, in one embodiment, with relativealignment such that the functional elements 102 are then released intothe template substrate. To reduce the adhesion of the dicing tape, UVrelease dicing tape could be used, and the UV exposure could be either aflood exposure, or through a stencil or mask so that only the adhesivetouching the chips that are to be transferred is UV-treated. As thedicing tape releases the functional elements 102, the elements 102 arereleased into the template substrate.

The layout of the wafer containing the functional elements 102 isimportant. For the transfer of many devices at one time, it ispreferable to layout the functional elements 102 on the wafer such thatthe spacing between every i functional elements 102 in the x axis andevery j functional elements 102 in the y axis matches the x and yspacing between holes on the punched web 108 to which the devices willbe transferred. If such a layout is not convenient or practical, thenthe transfer of the functional elements 102 could be completed in morethan one step, as described above. Analogously, the transfer of two ormore different functional elements 102 could be completed in asequential index and transfer process, as described above.

Another option would be to first cut the wafer in to square dies thatare tiled together (pick and place) to make a square area suitable fortransfer, then dice the functional elements 102 in the square alltogether. This would allow the most of the area of a round wafer. Itwould also avoid the need to layout the wafer in a special way fortransfer.

The equipment to accomplish a transfer process from a wafer or from afilled template is relatively similar. First, the equipment needs theappropriate web handling devices to smoothly transfer web into and outof the transfer process area. As described above, the transfer processarea comprises one or more transfer process assemblies. Each transferprocess assembly consists of the following basic components: 1. Atemplate or wafer holder on a movable stage; 2. The incoming laminatedweb; 3. A method for positioning the web and the template or wafer withrespect to each other; and 4. A transfer head for deforming the adhesivelaminate through the web such that it makes contact to the devices onthe wafer or in the template.

FIG. 14 illustrates that the equipment may include a web line of thefirst substrate 108, a template 128 for holding the second substrate104, and a transfer mechanism 130 having transfer heads 136 to allow forthe transfer of the functional elements 102 from the second substrate104 to the first substrate 108. The equipment may also includes one ormore registration stations 132 to allow the relative positioning of thefirst substrate 108 and the second substrate 104. A vacuum station 134may be used to hold the second substrate 104 in place. A storage 136 mayalso be included that holds the second substrate 104 that can betransferred onto the web line 128.

The stage for holding the wafer or the template could be a simple x, ystage, which holds the template or the wafer to it by means of a vacuum.This stage could be automatically translated after every transfer stepsuch that another set of devices are ready for transfer. The stage couldbe fed fresh wafers or templates automatically from a cassette of wafersor templates.

Alternatively, the transfer template could be a filled FSA web in theshape of a belt (which for example, is moved between rolls), whichprogresses underneath the adhesive laminated transfer web such that aset of IC devices is always ready for transfer as illustrated in FIG.15. The equipment in FIG. 15 is similar to the equipment in FIG. 14except an FSA station 135 is included.

The web could be positioned with respect to the transfer template or theIC wafer by the registration station 132 (e.g., a vision system) toalign reference marks on the template or wafer with complementaryreference marks on the webs. Alternatively, the vision system couldalign to the devices themselves, or to the punched holes on the laminateweb, or both.

The transfer head 136 could take many forms. It could be a set of pinslaid out in an arrangement to match the layout of the holes punched inthe substrate 104 web. Alternatively, it could be a shaped plate, madeout of plastic or metal, with protrusions that match the layout of theholes punched in the substrate 104 web. In yet another form, it couldsimply be a deformable bladder, which could be deformed with airpressure such that it deforms the adhesive laminate.

For the transfer head 136, it would be preferable to not have the web ofthe first substrate 108 touch the IC wafer or template except during thetransfer step itself. This could be accomplished by having the templateor wafer stage have z-motion capability, such that it can move down fromthe transfer position before the web for the first substrate 108 isindexed. Alternatively, the web could be held above the transfer stage.It could be held at a permanent height above, but close to, the templateor wafer stage, or it could have z-axis motion, such that it could bebrought into contact or close proximity of the template or wafer stage.Or a separate metal or plastic sheet or film could be placed between theweb and the transfer template or wafer to ensure that the sliding webdoes not come in contact with the template or wafer on the stage.

In alternative embodiments, any of the equipments shown in FIG. 14 orFIG. 15 (or alternative embodiments thereof) can include a fillingstation (not shown). The filling station that can be used to fill gapsthat may be formed in the openings in the first substrate after thefunctional elements are transferred. The filling station may be equippedwith a filler material such as a UV cured polymer or a thermoset polymeror a thermoplastic resin. In addition, the equipment may include anadhesive removal station where the adhesive film (which can be atemporary adhesive film) can be pealed off. In one embodiment, thetemporary adhesive is a UV release tape. In these embodiments, theinterconnections to the functional elements can be made by directlyscreen printing silver ink onto the functional elements' contact pads.One advantage for having a temporary adhesive film is that it eliminatesthe need for vias to establish interconnection to the functionalelements.

FIGS. 16–17 illustrate that in a further alternate embodiment, thesecond substrate 104 is flexible. The functional elements 102 may bedeposited into the second substrate 104, either by an FSA-process filledplastic template or devices on flexible dicing tape. The first substrate108, to which the functional elements 102 are transferred to can berigid or flexible depending on applications. In this embodiment, thefunctional elements 102 can be transferred to a first substrate 108,which in one embodiment, is rigid, such as a large or small IC device,silicon wafer, wafer of IC devices, glass, etc. The transferredfunctional elements 102 can be attached to the first substrate 108 usingeutectic solder or other flip-chip interconnect methodologies, or anadhesive layer on the substrate or device as discussed above, or acombination of techniques. During the transfer process, the rigid firstsubstrate 108 is positioned in close proximity to, and facing, thefunctional elements 102 holding side of the flexible second substrate104. The functional elements 102 are transferred to the first substrate108 by deflecting portions of the flexible second substrate 104 suchthat selected functional elements 102 are brought into contact with andattached to the first substrate 108.

As illustrated in FIG. 16, the second substrate 104 has a plurality offunctional elements 102 arranged in a densely packed array. Similar toabove, each of the functional elements 102 includes contact pads 122.The second substrate 104 is flexible. The functional elements 102 may becoupled to the second substrate 104 using methods such as FSA. The firstsubstrate 108, which in one embodiment, is rigid, includes a patternedconductive leads 138. The patterned conductive leads can be an antennaleads in one example. The first substrate 108 can be flexible. In oneexample, the first substrate 108 is a substrate that can support anantenna, such as one used for an RF ID tag. The first substrate 108 thuscan include antenna lead formed thereon. At least part of the antennalead may be the conductive leads 138 shown in FIG. 16.

As illustrated in FIG. 16, an adhesive layer 140 is disposed over thepatterned conductive lead 138. When the functional elements 102 aretransferred to the first substrate 108, the contact pads 122 will makeelectrical contacts to the conductive leads 138 either through viasformed into the adhesive layer 140 or by the conductivity characteristicof the adhesive layer 140. The adhesive layer 140 may be electricallyconductive and/or anisotropically conductive such that it is onlyconductive in one direction, (e.g., Z-direction). That way, the adhesivelayer 140 will allow electrical connection between the conductive lead138 on the first substrate and the contact pads 140 on the functionalelements 102.

In FIG. 16, a transfer mechanism 142 including at least one transfer pin144 is place under the second substrate 104. The second substrate 104 isplaced or held on a vacuum station 146 to hold the second substrate 104in place. The transfer mechanism 142 drives the transfer pin 144 intothe second substrate 104, which is flexible. The transfer pin 144 isable to push the functional elements 102 up toward the first substrate108 to transfer the functional elements 102 onto the first substrate108. FIG. 17 illustrates the functional elements 102 having beentransferred onto the first substrate 108.

In the alternative embodiment, the conductive leads 138 have adhesivecharacteristic such that the adhesive layer 140 can be eliminated. Inthis embodiment, at least the portion of the conductive leads 138 thatwill make contact to the contact pads 122 have adhesive material suchthat the can adhere to the contact pads 122 and allow mechanical as wellas electrical coupling.

While the preceding discussions have focused on the use of a transfermethod with the functional elements 102 such as integrated circuitsassembled using FSA, it is clear to those skilled in the art that such atransfer process can be used to assemble other types of functionalelements that are formed in arrays on one substrate, and thentransferred to another substrate.

For example, it is difficult and costly to form thin film transistorsover large areas on flexible substrates. Typically, processing equipmentgets very expensive for large area treatments, and few substrates canwithstand the processing temperatures and conditions necessary to formthin film transistors. One could inexpensively form small circuitelements on standard, small-to-medium sized substrates, singulated thecircuit elements, and then use this transfer process to spread thedevices over a large area, or place them on a flexible substrate.

As one example, it is possible to form amorphous or polysilicon TFTs onstainless steel foils. Such devices can be formed relativelyinexpensively today by using standard semiconductor or flat paneldisplay processing equipment. For example, a group at PrincetonUniversity routinely forms amorphous silicon TFTs on four inch steel“wafers” (or flats). The equipment cost is prohibitive, however, to forma similar TFT array on a substrate that is 1 meter across.

Using a version of the transfer method described here, however, TFTscould be formed on a wafer, flat, or ribbon on one substrate, andtransferred in a simple fashion to another. For example, a ribbon ofTFTs could be attached to a carrier substrate and then singulated. Thepurpose here is to simply hold the singulated transistor elements inplace. The transfer tool described here could then select TFTs off ofthis densely-packed ribbon and transfer them to the final substrate,placing them in an arbitrary pattern and spacing. If the adhesive layerhere is an anisotropically conductive adhesive, then interconnection tothe TFT (with the steel underlayer still in place) is easily donethrough the adhesive. Alternatively, vias through a nonconductiveadhesive can be used.

Transfer methods have been described in the past, typically by providingsome sort of sacrificial underlayer on the primary substrate, which isetched away to free a thin, fragile active circuit element. In thiscase, we take advantage of the ability to slit, cut, or otherwisesingulated the steel foil and then transfer the element as a whole.

Likewise, this approach could be extended to other substrates that couldbe singulated. Other circuit elements (besides integrated circuits),that could be transferred, include active elements, passive elements, oreven other functional systems, such as sensors (e.g., chemical orbiological sensors), MEMs, VCSELS, photodiodes, mechanical elements,thin film transistors, passive electrical elements, capacitors,inductors, resistors, diodes, optical elements, photodiodes, lightemitters, microprocessors, memory structures, radio frequencytransceivers, communications elements, power sources, energy storages,electromagnetic radiation emitting elements, electromagnetic radiationreflecting elements, and display elements (e.g., display pixel elementsand display drivers), to name a few.

It is to be appreciated that many of the embodiments discussed thetransferring of the functional elements from one substrate (e.g.,substrate 104) to another substrate (e.g., substrate 108) in a webformat. But, the embodiments are similarly applicable to other formatsuch as sheet format. Thus, instead of the substrate 104 and thesubstrate 108 being in the web formats (e.g., roll-to-roll), thesubstrate 104 and the substrate 108 are in sheet forms.

Some of the embodiments described can be used to form the strap assemblydescribed in patent application Ser. No. 09/872,985, now U.S. Pat. No.6,606,247 which is hereby incorporated by reference.

1. A method for assembling a device comprising: placing a functionalelement in a first opening formed in a template substrate using afluidic self-assembly process (FSA) and a web process; and transferringthe functional element to a device substrate having a second openingformed therein wherein the functional element is held within the secondopening and against an adhesive film coupled to the top of the devicesubstrate, wherein said transferring includes pressing the adhesive filmthrough the second opening so that an adhesive side of the adhesive filmadheres to the functional element through the second opening andtransfers the functional element out of the first opening in thetemplate substrate into the second opening of the device substrate. 2.The method of claim 1 further comprising: forming at least oneinterconnection to the functional element.
 3. The method of claim 1wherein the adhesive film is at least one of a dielectric film, apressure sensitive adhesive, a heat-activated adhesive,chemically-activated adhesive, microwave frequency activated adhesive,radio frequency activated adhesive, radiation-activated adhesive, alaser ablatable adhesive, and an anisotropically-conductive adhesive andwherein the adhesive film is placed over the device substrate andwherein said second opening is formed completely through the devicesubstrate.
 4. The method of claim 3 wherein the adhesive film is adielectric film and the method further comprises: forming a via throughthe dielectric film to allow for an electrical connection to thefunctional element.
 5. The method of claim 4 further comprising: formingan electrical connection to the functional element.
 6. The method ofclaim 1 further comprising: forming a conductive trace on a surface ofthe device substrate; and interconnecting the conductive trace to thefunctional element.
 7. The method of claim 1 wherein the conductivetrace is formed on top of the adhesive film.
 8. The method of claim 6wherein the interconnecting of the conductive trace to the functionalelement is accomplished through a via created in the adhesive film. 9.The method of claim 6 wherein the interconnecting of the conductivetrace to the functional element is accomplished through the adhesivefilm, wherein the adhesive film is an anisotropically conductiveadhesive.
 10. The method of claim 1 further comprising: forming anantenna trace on the surface of the device substrate; andinterconnecting the antenna trace to the functional element.
 11. Themethod of claim 10 wherein the antenna trace is formed on top of theadhesive film.
 12. The method of claim 10 wherein the functional elementis a radio frequency control element.
 13. The method of claim 10 whereinthe interconnecting of the conductive trace to the functional element isaccomplished through a via created in the adhesive film.
 14. The methodof claim 10 wherein the interconnecting of the conductive trace to thefunctional element is accomplished through the adhesive film, whereinthe adhesive film is an anisotropically-conductive adhesive.
 15. Themethod of claim 1 further comprising: placing, using said FSA process, aplurality of said functional elements in a plurality of said firstopenings formed in the template substrate; transferring at least onefunctional element selected from the plurality of functional elements tothe second opening formed in the device substrate.
 16. The method ofclaim 15 wherein the plurality of first openings in the templatesubstrate are in one or more regular patterns designed to match apattern of the second openings in the device substrate.
 17. The methodof claim 15 wherein the plurality of first openings in the templatesubstrate are in one or more arrays designed to match an array patternof the second openings in the device substrate.
 18. The method of claim15 wherein the plurality of first openings in the template substrate arein an array in which a pitch between the first openings in an orthogonaldirection is equal to a corresponding pitch of the second openings inthe device substrate.
 19. The method of claim 15 wherein the pluralityof first openings in the template substrate are in an array in which apitch between the first openings in an orthogonal direction is equal toa corresponding pitch of the second openings divided by an integernumber.
 20. The method of claim 1 wherein the template substrate isselected from a group consisting of a silicon wafer, a plastic film, aglass sheet, and a multilayer film comprising a combination thereof. 21.The method of claim 1 wherein functional element is an integratedcircuit.
 22. The method of claim 1 further comprising: filling a gap inthe second opening in the device substrate.
 23. The method of claim 22wherein filling a gap in the second opening in the device substrate isaccomplished with at least one of UV-curable epoxy, and thermoset resin.24. The method of claim 1 further comprising: laminating the adhesivefilm over a surface of the device substrate prior to the transferring ofthe functional element.
 25. The method of claim 1 further comprising:laminating additional films over a surface of the device substrate. 26.The method of claim 1 further comprising: forming at least one of a topcontact and a bottom contact on the functional element.
 27. The methodof claim 1 further comprising: forming electrical interconnection to atleast one of the top contact and the bottom contact on the functionalelement.
 28. A method for assembling a device comprising: transferring afirst functional element to a device substrate having a first openingformed therein, the first functional element is held within the firstopening and against an adhesive film coupled to the top of the devicesubstrate and the first functional element is transferred to the firstopening from a first template substrate having the first functionalelement deposited therein; and transferring a second functional elementto the device substrate having a second opening formed therein, thesecond functional element is held within the second opening and againstthe adhesive film coupled to the top of the device substrate and thesecond functional element is transferred to the second opening from asecond template substrate having the second functional element depositedtherein; wherein transferring the first functional element to the firstopening comprises pressing the adhesive film through the first openingso that an adhesive side of the adhesive film adheres to the firstfunctional element and transfers the first functional element out of thefirst opening in the template substrate into the first opening of thedevice substrate transferring of the first functional element tc thedevice substrate; and transferring the second functional element to thesecond opening comprises pressing the adhesive film through the secondopening so that an adhesive side of the adhesive film adheres to thesecond functional element and transfers the second functional elementout of the second opening in the second template substrate into thesecond opening of the device substrate.
 29. The method of claim 28wherein the first functional element and the second functional elementis at least one of different material from one another, differentfunctionality from one another, different shape from one another, anddifferent size from one another.
 30. The method of claim 28 wherein thefirst functional element and the second functional element is selectedfrom a group consisting of thin film transistor, passive electricalelement, capacitor, inductor, resistor, diode, optical element,photodiode, light emitter, and microelectronic mechanical system (MEMS),microprocessor, memory structure, radio frequency transceiver,communications element, sensor, power source, energy storage,electromagnetic radiation emitting element, electromagnetic radiationreflecting element, display driver, display pixel element, and displayelement.
 31. The method of claim 28 wherein the first functional elementis deposited in the first template substrate using fluidic-self assemblyprocessing.
 32. The method of claim 28 wherein the second functionalelement is deposited in the second template substrate using fluidic-selfassembly processing.
 33. A method for assembling a device, the methodcomprising: placing a plurality of functional elements in acorresponding plurality of first openings formed in a first substrate;transferring only a portion of said plurality of functional elements toa second substrate having at least one second opening, wherein anadhesive film is coupled to the top of said second substrate and havingat least a portion exposed in said at least one second opening in saidsecond substrate and wherein said transferring comprises pressing saidadhesive film through said second opening such that an adhesive side ofsaid adhesive film adheres to the portion of said plurality offunctional elements and transfer the portion of said plurality offunctional elements out of its location in the plurality of firstopenings in the first substrate to said at least one second opening inthe second substrate.
 34. The method of claim 33 wherein the placingcomprises a fluid self assembly process wherein a slurry of functionalelements is created and dispensed over the first substrate and thefunctional elements become disposed in the first openings; and whereinthe transferring comprises preventing at least one functional elementfrom being transferred to the second substrate.
 35. The method of claim33 further comprising: aligning the first substrate to the secondsubstrate so that only the portion is transferred.
 36. The method ofclaim 33 wherein the transferring occurs at a first time and wherein themethod further comprises a further transferring of another portion ofthe plurality of functional elements from the first substrate to thesecond substrate.
 37. The method of claim 1 wherein the adhesive film isa temporary adhesive film.
 38. The method of claim 37 further comprisefilling a gap in the second opening in the device substrate and removingthe adhesive film.
 39. The method of claim 28 wherein the adhesive filmis a temporary adhesive film.
 40. The method of claim 39 furthercomprising: filling a gap in the second opening in the device substrateand removing the adhesive film.
 41. The method of claim 7 wherein theinterconnecting of the conductive trace to the functional element isaccomplished through a via created in the adhesive film.
 42. The methodof claim 7 wherein the interconnecting of the conductive trace to thefunctional element is accomplished through the adhesive film, whereinthe adhesive film is an anisotropically conductive adhesive.
 43. Amethod for assembling a device comprising: transferring a functionalelement to a device substrate having an opening formed therein whereinthe functional element is held within the opening and against anadhesive film coupled to the device substrate, and wherein thefunctional element is transferred from a plurality of functionalelements that are disposed on a handle substrate format and temporarilyheld in place on the handle substrate, wherein the adhesive film iscoupled to the top of said device substrate and having at least aportion over the opening exposed to contact said functional element andwherein said transferring comprises pressing said exposed adhesive filmover the opening toward said handle substrate such that an adhesive sideof said adhesive film adheres to said functional element and transferssaid functional element disposed on the handle substrate into theopening of said device substrate.
 44. The method of claim 43 furthercomprises releasing the functional element from the handle substrate.45. The method of claim 43 further comprising: interconnecting aconductive trace to the functional element.
 46. The method of claim 45wherein the conductive trace is one of formed on top of the adhesivefilm and formed on a surface of the device substrate.
 47. The method ofclaim 45 wherein the interconnecting of the conductive trace to thefunctional element is accomplished through a via created in the adhesivefilm.
 48. The method of claim 45 wherein the interconnecting of theconductive trace to the functional element is accomplished through theadhesive film, wherein the adhesive film is an anisotropicallyconductive adhesive.
 49. The method of claim 43 further comprising:interconnecting an antenna trace to the functional element.
 50. Themethod of claim 49 wherein the antenna trace is one of formed on top ofthe adhesive film and formed on a surface of the device substrate. 51.The method of claim 49 wherein the functional element is a radiofrequency control element.
 52. The method of claim 49 wherein theinterconnecting of the conductive trace to the functional element isaccomplished through a via created in the adhesive film.
 53. The methodof claim 49 wherein the interconnecting of the conductive trace to thefunctional element is accomplished through the adhesive film, whereinthe adhesive film is an anisotropically-conductive adhesive.
 54. Amethod for assembling a device comprising: transferring a functionalelement to a first opening in a template substrate, the first openingselected from a set of openings formed on the template substrate, thefunctional element selected from a set of functional elements that aredisposed on a handle substrate and temporarily held in place on thehandle substrate, the set of openings having a pattern matching thepattern of the set of functional elements on the handle substrate; andtransferring the functional element from the first opening to a secondopening formed therein in a device substrate, the device substratehaving an adhesive film coupled thereto, the adhesive film holding thefunctional element against the second opening; wherein the adhesive filmis coupled to the top of said device substrate and having at least aportion exposed to contact said functional element and wherein saidtransferring comprises pressing said adhesive film toward said handlesubstrate such that an adhesive side of said adhesive film adheres tosaid functional element and transfers the functional element from thehandle substrate to said device substrate.
 55. The method of claim 54further comprises releasing the functional element from the handlesubstrate.
 56. The method of claim 54 further comprising:interconnecting a conductive trace to the functional element.
 57. Themethod of claim 56 wherein the conductive trace is one of formed on topof the adhesive film and formed on a surface of the device substrate.58. The method of 56 wherein the interconnecting of the conductive traceto the functional element is accomplished through a via created in theadhesive film.
 59. The method of claim 56 wherein the interconnecting ofthe conductive trace to the functional element is accomplished throughthe adhesive film, wherein the adhesive film is an anisotropicallyconductive adhesive.
 60. The method of claim 54 further comprising:interconnecting an antenna trace to the functional element.
 61. Themethod of claim 60 wherein the antenna trace is one of formed on top ofthe adhesive film and formed on a surface of the device substrate. 62.The method of claim 60 wherein the functional element is a radiofrequency control element.
 63. The method of claim 60 wherein theinterconnecting of the conductive trace to the functional element isaccomplished through a via created in the adhesive film.
 64. The methodof claim 60 wherein the interconnecting of the conductive trace to thefunctional element is accomplished through the adhesive film, whereinthe adhesive film is an anisotropically-conductive adhesive.